1. Technical Field
This invention relates to a wet-based, wood-burning boiler.
2. Background Art
The prior art, U.S. Pat. No. 567,034, discloses heating stove; U.S. Pat. No. 1,305,764 discloses a means for converting base burner stoves into soft coal heaters; U.S. Pat. No. 2,559,271 discloses a fireplace with movable reflector; U.S. Pat. No. 4,154,212 discloses a fuel burning heater; U.S. Pat. No. 4,192,285 discloses an air tight fuel burning stove; and U.S. Pat. No. 4,320,738 discloses a heating stove.
When wood burns, a mixture of combustible gases, water vapor and carbon dioxide leave the fire as flue gas. Excellent combustion (complete burning) produces a flue gas composed almost entirely of water vapor and carbon dioxide. A very hot fire, supported by sufficient oxygen, approaches complete combustion.
There are three stages of combustion. In the first stage, the wood is heated to evaporate and drive off moisture in the wood. This heat does not warm the boiler, stove, room or chimney. In the second stage, the wood starts to break down chemically at 500.degree. F. and volatile matter is vaporized. These vapors contain 50-60% of the heat value of the wood. If the temperature reaches 1100.degree. F. and oxygen is added, these vapors will burn. In the third stage, following the release of the volatile gases, the remaining material is charcoal, which burns at temperatures exceeding 1100.degree. F.
Flue gases leaving the fire cool as heat is absorbed by the smokepipe-chimney system. It flue gas temperature drops below about 270.degree. F. at the top of the chimney, these unburned volatiles and water vapor condense. In time, the water evaporates leaving dark, highly combustible creosote on the smokepipe and chimney walls.
Creosote presents considerable danger. It is the highly combustible fuel that feeds a chimney fire. These fires produce flying embers and the intense heat can crack the tile linings, deteriorate masonry, and ruin a metal chimney. In some cases, violent vibration, caused by repeated ignition and suffocation of the burning creosote, can separate the smokepipes, and dump burning material over a large area. A fire within the chimney can also spread to house framing and endanger lives as well as property.
A factor that can affect creosote formation is the smokepipe or stovepipe. The length of the smokepipe should be kept as short as possible and always less than 10 feet. A long run of smokepipe will radiate more heat, but it will cool flue gases enough to increase creosote formation.